The invention relates to the measuring of a phase shift between an external periodic signal that is applied to an electronic component, and an internal signal with which data are to be outputted at one or more outputs of an electronic component.
Electronic components are often synchronously driven; i.e., data are routed from one component to the next according to a clock signal. However, the importance of signal transit times and transit times of clock signals must not be overlooked, particularly for electronic components that are driven with high frequencies. In order to adapt the processing of data to the signal delays conditioned by the transit times, internal reference clock signals exhibiting a phase shift relative to the external clock signals are generated in the electronic components. The phase shift can derive from internal signal transit times in the electronic component and is strongly dependent on technology-related fluctuations.
In order to be able to correctly evaluate the output data in the testing of the electronic component, it is necessary to determine the phase shift between the external clock signal and the internal clock signal according to which the data are synchronously outputted by the electronic component.
In known testing systems, a time xcex94t0 is customarily determined in order to measure the phase. xcex94t0 is a time difference by which an evaluation signal of the testing device must be shifted relative to the clock signal of the testing device in order to correctly logically evaluate a data signal or an internal clock signal. The transition of the signal from xe2x80x9c0xe2x80x9d to xe2x80x9c1xe2x80x9d or vice versa is needed for this. In order to measure xcex94t0, the evaluating signal of the testing device is varied until the transition between the two voltage levels of the signal has been found. The search process is time-intensive and must be performed for each data signal and the internal clock signal.
It is accordingly an object of the invention to provide a method and a device for measuring the phase shift between a periodic signal and an output signal at an output of an electronic component which overcome the above-mentioned disadvantages of the prior art methods and devices of this general type, in which the device provides an improved method with which the phase shift between the external clock signal and the internal clock signal (that is to say, the output data signal) in electronic components, particularly in the testing of the electronic component, can be determined.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for measuring phase shifts. The method includes providing an output driver having an output and a switching device connected to a supply voltage and to the output. An output signal is applied to the output driver. The supply voltage is switched through to the output in dependence upon the output signal. A periodic signal is applied to the output of the output driver. A current through the switching device is measured and a phase shift between the periodic signal and the output signal is determined in dependence on the current measured.
According to a first aspect of the invention, a phase-sensitive measuring element is utilized for measuring the phase shift between the periodic signal and the output signal. The phase-sensitive measuring element is configured to measure an electrical quantity representing an average value of the phase shift.
The advantage of utilizing a phase-sensitive measuring element is that the phase shift between the periodic signal and the output signal can be determined more exactly. In the prior methods, the phase shift is determined by timing, with the measured time being considered in relation to the period duration of the clock signal.
At very high clock signal frequencies, the timing is generally imprecise, because it is carried out by single measurements in discrete steps. The imprecision is determined mainly by the imprecision of the individual measurement steps and the size of the discrete steps. Another advantage is that the phase shift is automatically detected, and the value of the phase shift can be evaluated as an electrical quantity, for instance in the testing device, without unnecessarily prolonging the testing sequence by an expensive measuring sequence.
According to another aspect of the invention, a method is provided for measuring the phase shift between the periodic signal and the output signal at an output of an electronic component. The output signal is applied to an output driver. The output driver contains a switching device, which is connected to a supply voltage and the output, it being possible to switch the supply voltage through to the output in dependence upon the output signal. The periodic signal is applied to the output. The current through the switching device is measured, and the phase shift between the periodic signal and the output signal is calculated as a function of the measured current.
In accordance with an added mode of the invention, the current measured is averaged which gives a more reliable result.
In accordance with an addition mode of the invention, there are the steps of using an external clock signal as the periodic signal and using an internal clock signal for the output signal.
In another aspect of the invention, a device is provided for measuring the phase shift between the periodic signal and the output signal that can be applied at an output of an electronic component by an output driver. The output driver contains a switching device that is connected to a supply voltage terminal and to the output in order to switch the supply voltage terminal through to the output in dependence upon the output signal. The device contains a drive circuit for applying the periodic signal to the output of the electronic component. The device further contains a supply voltage source, which can be connected to the supply voltage terminal of the electronic component by way of a current measuring device. In this manner, the phase shift between the periodic signal and the output signal can be measured as in dependence on a current that is measured with the aid of the current measuring device.
The advantage of the invention is the possibility, in conventional testing devices, to measure the current flow into and out of the supply voltage inputs, on one hand, and to connect the terminals of the testing device to the electronic component in such a way that a signal can be driven to an output of the electronic component, on the other hand. This is possible because each connection to the testing device can be driven as an input and as an output under the control of the respective test program. In this manner, it is possible to determine the phase shift from the quantity of the current flowing into the supply voltage input.
In prior methods, the phase shift is performed by a timing operation, whereby the measured time is considered in relation to the period duration of the clock signal, and the phase shift is determined therefrom. In contrast, the present method has the advantage that it can be applied even given very high clock signal frequencies, i.e. given very small period durations. The timing operations become imprecise as the time differences to be measured become smaller, and therefore the phase shift can no longer be precisely measured. In contrast, the inventive method and device have the advantage that, the phase shift over several periods is automatically averaged, and the method is precise even given high frequencies and small phase shifts.
In a preferred embodiment, it is provided that a supply voltage input of the switching device is connected to a capacitance component, whereby an additional output of the capacitance component is connected to a fixed voltage potential. The capacitance component smoothes the current shape, thereby making it possible better to determine the average value of the phase shift.
In accordance with an added feature of the invention, a terminal for carrying a constant d.c. voltage potential is provided. A capacitance component having a first terminal is coupled to the supply voltage terminal and a second terminal is connected to the terminal carrying the constant d.c. voltage potential.
In accordance with another feature of the invention, a testing device is provided which contains the drive circuit.
In accordance with an additional feature of the invention, the supply voltage terminal is one of two supply voltage terminals each supplying a supply voltage, and the switching device is connected between the two supply voltage terminals.
In accordance with a further feature of the invention, the switching device has a transistor.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of measuring a phase shift. The method includes providing a phase-sensitive measuring element, and supplying the phase-sensitive measuring element with a periodic signal and an output signal. The output signal is provided at an output of an electronic component connected to the phase-sensitive measuring element. The phase-sensitive measuring element is used to measure an electrical quantity representing an average value of the phase shift between the periodic signal and the output signal.
In accordance with an added mode of the invention, there are the steps of measuring a voltage as the electrical quantity, and providing the phase-sensitive measuring element with a voltage measuring device for measuring the voltage.
In accordance with another mode of the invention, there is the step of providing the phase-sensitive measuring element with an exclusive-or gate with two inputs, the two inputs receiving the periodic signal and the output signal.
In accordance with a concomitant mode of the invention, there is the step of providing the phase-sensitive element with an analog phase detector containing a step recovery diode.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and a device for measuring the phase shift between a periodic signal and an output signal at an output of an electronic component, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.